How Batman and Robin embarrassed the Palace, Scotland Yard and the government

They had thought carefully about the best way to infiltrate what is supposed to be one of the most secure buildings in Britain. The activists had tagged on to parties of tourists being shown around Buckingham Palace; they had examined aerial maps and plans of the locality; and they had monitored security patrols around the building.

In the end, Fathers4Justice took the most direct route. Dressed as Batman and Robin, Jason Hatch and Dave Pyke stepped over a metre-high fence, propped a ladder against the corner of the palace and climbed up.

Neither expected to make it but, to the delight of the group's leaders and the acute embarrassment of the palace, Scotland Yard and the government, Mr Hatch - aka a rather portly Batman - managed to scramble up the ladder.

He then edged around to the front of the building a few metres from the main balcony, where the royal family congregates on state occasions, and unfurled a banner proclaiming the group's message.

Within moments the group's founder, Matt O'Connor, was on news channels describing the stunt and the rationale behind it. Minutes later the television satellite vans arrived and, just as the group had hoped, the episode was being broadcast around the world.

The incident is a huge embarrassment to those charged with making sure security surrounding the royal family and other prominent figures is adequate.

Security around the royals was reviewed after the Daily Mirror reporter Ryan Parry got a job as a palace footman before a state visit by George Bush. It also came under scrutiny after "comedy terrorist" Aaron Barschak gate-crashed Prince William's 21st birthday party at Windsor Castle in June 2003.

But concerns will go deeper - at a time of heightened fears over terrorism, such a breach is a huge blow to the security services.

Yesterday's events began shortly before 2pm, when a car carrying Mr Hatch, a 32-year-old painter and decorator from Cheltenham, Mr Pyke and an extendible aluminium ladder stopped on Constitution Hill. The "caped crusader" and "boy wonder" leapt out and jumped over the small fence. Their accomplices passed the ladder over to them.

Other activists climbed on to ornate gates at the front of the palace to create a diversion while Mr Hatch, described as a "national operations co-ordinator" for the group, and Mr Pyke, also a veteran of direct action protests, leaned the ladder against the corner of the building, next to a security camera. The campaigners claim armed police officers rushed over, pointed their weapons at the pair and ordered them to stop. Mr Hatch and Mr Pyke shouted that they were Fathers4Justice activists, not terrorists. Mr Pyke decided to climb down but Mr Hatch continued.

There was confusion among Palace officials. A startled Buckingham Palace spokesperson said: "There's a man there ... I'm not sure where he is but I can hear him shouting."

Mr Hatch had, in fact, managed to scramble along a 15cm-wide ledge and over a gate which the royal family often uses, one of the most secure parts of the palace. He had edged past offices, empty state rooms - the Queen is in Balmoral - and finally stationed himself near the balcony, where Prince Charles shared a kiss with Princess Diana on their wedding day.

There he stopped and unfurled his banner, which read: "Super dads of Fathers4Justice ... Fighting for the right to see your kids." The whole operation took less than a minute.

While Mr Hatch (nicknamed Escape Hatch by his fellow protesters) spoke to police negotiators stationed on the balcony and asked to speak to the Queen, other members fleshed out the details.

Mr O'Connor said plans for yesterday's coup had been finalised in a pub in Shropshire on Saturday. He explained that the group had already targeted the state, when condoms full of purple flour were hurled at Tony Blair during prime minister's questions, and the church when activists, including Mr Hatch, climbed on top of York Minster. The royal family was the next logical target.

He said: "Their crest is in every court and it is the court which [is] failing to ensure that fathers get the access to their children which they are legally entitled to."

Yesterday's events coincided with the appearance of two Fathers4Justice activists at Bow Street magistrates court in connection with the flour attack.

It is a time of increased activity by the group. At the weekend, another protester, David Chick, caused chaos when he climbed to the top of the London Eye dressed as Spiderman.

Back at Buckingham Palace, Robin - Mr Pyke - turned up. Extraordinarily, he had not been held by the police but was allowed to wander back in front of the palace, still dressed in his costume, and give his story.

Mr Pyke, 48, also from Cheltenham, said: "This was a very odd thing. I came down the ladder and I was waiting for police officers to jump on me but nothing happened. Nobody seemed to be taking any notice."

He walked into a park, put on a cap and slipped away. Mr Pyke, who is unhappy that the courts have given his former wife custody of their two children, said: "I had a bag with me - there could have been anything in there, explosives or anything. We are totally untrained, just ordinary guys. If we can get in there, anyone can."

The Metropolitan police commissioner, Sir John Stevens, disagreed, saying that the pair would have been shot if officers had thought they were terrorists.

It was only after he had given media interviews that Mr Pyke was led away.

Meanwhile, Mr Hatch stayed put. He accepted drinks of orange squash - a tactic sometimes used by the police to encourage protesters to surrender in order to answer the call of nature. He was lowered to the ground by two police officers in a cherry picker five hours later.

Fellow activists said he had never intended to get on to the balcony because it would have been too easy to remove him. The campaigners knew police would have to stand off - if they tried to grab him he could have fallen from the ledge.

Mr O'Connor said the public could look forward to more "spectaculars".

"We have been thinking creatively and laterally about what to do next. We have got some very surprising events planned. The government should be worried. However, this is going to be the last of the superhero stunts. I don't think we could better this," he said.

Fathers 4 Justice Protests

December 2002 Two coachloads of Santas occupy Lord Chancellor's Department

February 2003 Campaigners dressed as Elvis present inflatable heart to president of Family Division, Dame Elizabeth Butler-Sloss

May 2003 Two members stage roof-top protest at Plymouth county court wearing Tony Blair masks

October 2003 Dave Chick, dressed as Spider-Man, climbs crane near Tower Bridge. Six-days of chaos as police close roads

February 2004 Activists scale bridges and gantries in London, Bristol and Newcastle